1. Field of the Invention
The present invention is directed to a filter for use with an aquarium, and more particularly, to a canister filter.
2. Description of the Related Art
As described in U.S. Pat. No. 3,273,717 to Canterbury entitled "Combination Filter and Aerator," one type of aquarium filter, often referred to as a "nesting" type canister filter, includes a lower unit having a motor contained therein and an upper unit containing a filter cartridge. The upper unit mates with the lower unit which is designed to rest on a flat surface adjacent the tank. Additionally, the upper unit contains a pump section having a rotatable impeller which is driven by the motor. The bottom of the upper unit is closed in order to allow the upper unit to be removed for cleaning and filter replacement. As the bottom of the upper unit is closed, there is no direct contact between the motor and the impeller. Typically, the motor and impeller are magnetically coupled as shown in the '717 patent. U.S. Pat. No. 4,601,821 to Sherman et al., entitled "Freestanding Aquarium Filter," discloses an improved magnetic coupling which can substantially improve filter efficiency.
One of the major problems associated with "nesting" type canister filters is that water flow paths within canister filters are often asymmetrical such that clamping forces required for proper sealing are often not evenly distributed. Therefore, many prior art canister filters employ a plurality (four or more) of screws or retaining clips around the periphery of the cover to provide a tight seal at all points around the cover notwithstanding asymmetric loads on the cover. Consequently, it is often difficult to remove the cover from the canister to clean the filter.
Further problems associated with prior art canister filters are related to the use of flexible hoses to transport water between the tank and the filter. First, flexible hoses are generally relatively expensive and difficult to install. Second, in addition to the fact that over time they usually deteriorate, crack and leak, flexible hoses are frequently damaged when packaged by the manufacturer. Finally, flexible hoses can complicate cleaning because they often retain water after the filter has been stopped.
Still further, in many prior art canister filters the discharge tube passes between the canister wall and the filter cartridge. As a consequence, there is a significant reduction in the canister space available for the filter media.